Gerry Adams and Martin McGuinness must have the decency to finally come clean and tell the truth about a British government offer which might have saved the lives of six hunger strikers, an-ex IRA prisoner has said.

Richard O'Rawe, the former public relations officer for the H-block hunger strikers, has launched a new book which contains fresh evidence that a deal was possible after just four hunger strikers had died.

"When I wrote my first book five years ago, I was a lone voice in the wilderness," he said. "Since then, the evidence has piled up and many former republican prisoners have rallied to support my position.

"The facts are irrefutable. The offer the British made to the Sinn Féin leadership in July 1981 wasn't relayed to the hunger strikers or their families. The reason is clear: to have Owen Carron elected Fermanagh and South Tyrone MP and to kick off the move into electoral politics.

"Those who kept the offer secret didn't really care if the hunger strikers lived or died. That isn't a conclusion I wanted to reach but it's the only one possible when the evidence is put together."

O'Rawe's 2005 book, Blanketmen (Lilliput, €11.99), caused controversy when he revealed that Bik McFarlane, the IRA's commander in the jail, told him of a secret British offer which effectively granted the prisoners' five demands, except free association.

O'Rawe said he and McFarlane were delighted and McFarlane wrote to Gerry Adams accepting the offer. However, word came back from Adams that the Army Council thought the proposal inadequate and advised the prisoners to await a second offer – which never came.

"When my book was published Bik vehemently denied there had been an offer and that we had any such conversation. Last year, Bik found his memory. He admitted there was an offer and we had talked about it," O'Rawe said.

"Another IRA prisoner, Gerard 'Cleaky' Clarke, has revealed that he heard our conversation, as has another blanketman who has told this to the families of three hunger strikers.

"Gerry Adams, Martin McGuinness and other Sinn Féin figures hid the document containing the British offer from the hunger strikers. But it was uncovered through a Freedom of Information request."

Two sources at IRA Army Council level told O'Rawe that Adams had never even informed the Army Council of the British offer.

O'Rawe said those Sinn Féin leaders who knew of the offer must apologise to the hunger strikers' families for "what may well be the biggest cover-up in the history of republicanism".